This study investigated the effect of language immersion in an English-speaking environment on the production of intonational features in L2 English sentences. It was hypothesized that the Korean group who had been immersed in the English language as children would have intonation patterns more similar to native English speakers than a nonimmersed group of Korean speakers, who shared otherwise similar experience and proficiency with English. Sixty subjects in three groups--20 Korean adults in the immersed group, 20 Korean adults in the nonimmersed group, and 20 native English speakers (as a control group)--took part in the experiment. The immersed group was more native-like by having a steeper F0 declination tilt (a wider F0 range and a fast speech rate). However, the immersed group, like non-immersed group, exhibited difficulty in resetting F0 between adjacent phrases at boundary. These results suggest that the acquisition of second language (L2) intonation is affected by early immersion in an L2 environment, but the degree of intonational acquisition was shown to vary by subareas, in which some F0-related cues proved to be hard to acquire.